Ras Inhibitor CAPRI Enables Neutrophils to Chemotax Through a Higher-Concentration Range of Gradients

Abstract

Neutrophils sense and migrate through an enormous range of chemoattractant gradients through adaptation. Here, we reveal that, in human neutrophils, Calcium-promoted Ras inactivator (CAPRI) locally controls the GPCR-stimulated Ras adaptation. Human neutrophils lacking CAPRI (caprikd) exhibit chemoattractant-induced non-adaptive Ras activation; significantly increased phosphorylation of AKT, GSK3/3{beta}, and cofilin; and excessive actin polymerization. caprikd cells display defective chemotaxis in response to high-concentration gradients but exhibit improved chemotaxis in low- or subsensitive-concentration gradients of various chemoattractants as a result of their enhanced sensitivity. Taken together, our data reveal that CAPRI controls GPCR activation-mediated Ras adaptation and lowers the sensitivity of human neutrophils so that they are able to chemotax through a higher concentration range of chemoattractant gradients. Significance StatementNeutrophils provide first-line host defense by migrating through chemoattractant gradients to the sites of inflammation. Inappropriate recruitment and mis-regulated activation of neutrophils contribute to tissue damage and cause autoimmune and inflammatory disease. One fascinating feature of chemotactic neutrophils is their ability to migrate through an enormous concentration range of chemoattractant gradients (10-9 [~] 10-5 M) through "adaptation," in which cells no longer respond to the present stimuli, but remain sensitive to stronger stimuli. The inhibitory mechanism largely remains elusive, although many molecules of the excitatory signaling pathway have been identified. Our study reveals, for the first time, that the inhibitory component, CAPRI, is essential for both the sensitivity and the GPCR-mediated adaptation of human neutrophils.